The present invention relates to a vibration responsive mechanism for providing a required control output for another device or system to be controlled responsive to vibration such as an earthquake.
In a conventional earthquake responsive automatic fire-extinguishing device mounted on a space heater such as a kerosene heater which is actuated if an abnormal vibration such as an earthquake occurs, there has been widely used an inverted pendulum type vibration responsive mechanism using the fall of a weight. In this case there is an advantage that the response characteristic is stable since the kinematic factors of the pendulum are almost constant. However, this type of device has a disadvantage in that a response to vibration having a great amplitude as a whole, but having a low horizontal amplitude component such as a vertical hypocentre earthquake, can not be expected due to limitations inherent in its mechanism. There is disclosed a system in which a weight falls on a horizontal receptacle having a relatively small area in Japanese Patent Publication No. 19073/1969. This system is principally equivalent to the former system. Accordingly it has also similar advantages and disadvantages. This system will be referred to as a first system, as well as the former system.
There is another system belonging to typical weight suspension pendulum type in which a weight does not fall. For example, Japanese Utility Model Publication No. 39218/1973 discloses a fire-extinguishing system including a weight of a pendulum which is suspended through a coil spring and a permanent magnet in which when the displacement of the weight due to vibration exceeds a predetermined threshold, electrical contacts are closed by a magnetic force for effecting a control output by means of a servo-mechanism which is referred to broadly, as a relay thereby extinguishing the flame. This system will be referred to as a second system. This system can not prevent deterioration with age or deterioration in elasticity of a spring which is constantly subject to a direct load of a weight. However, it has similar advantages comparable to those of the first system in practical use. Furthermore, this has also an advantage that it is responsive to any vibration without the disadvantage involved in the first system. However, this system has two difficulties in maintenance cost and stability of said servomechanism for a long term.
Referring to the social trends relating to afore-mentioned fire-extinguishing systems, the use of a kerosene space heater having no earthquake responsive extinguishing means has been prohibited since July the first, 1977 in Tokyo by revision of fire protection regulations effective on October 1971. When an earthquake of the 4th degree on the seismic scale took place in Tokyo on Dec. 29, 1976, it was found from the records of the Metropolitan Fire Board that only 16% of all said earthquake responsive systems actually actuated in response to the vibration. Although the revised regulations require positive response at the 5th degree on the seismic scale it can be guessed that the response to earthquake is not sufficient yet in consideration of such ratio of responded systems. The Asahi News Paper dated Nov. 7, 1976 said that the Metropolitan Fire Board prepared a search report that there were 2.65 million kerosene space heaters in Tokyo at the end of the year 1975 whereas 1.18 million heaters (44.5%) were not provided with a fire-proof system. On Oct. 22, 1976, a TV news program of NHK reported that the attachment of such a system to currently used kerosene space heaters is technically difficult and the cost of the attachment is relatively high in comparison with the purchase cost of a new kerosene space heater provided with a fire-proof system.
When we consider the recent unusual cold weather and frequent earthquakes in the Northern hemisphere, and the low economical cost of kerosene in comparison with those of the other energy sources, such fire-proof systems must be a problem not only in overpopulated big cities such as Tokyo, or in Japan where there are relatively less fire-and-quake-proof buildings, but is a problem all over the world.
It is, therefore, one object of the present invention is to provide a vibration responsive mechanism which contributes to safety against accidental shock or vibration as well as earthquake, by providing said mechanism with advantages involved by the first and second systems and eliminating all disadvantages.
Another object of the present invention is to provide a vibration responsive mechanism which may readily be attached to a currently used system to be controlled, such as a kerosene space heater for forming an earthquake-proof automatic fire extinguishing device which is responsive to vibrations such as earthquake.
Further, another object of the present invention is to provide a novel type eccentricity variable thrust bearing which engages with and disengages from a thrust shaft in response to a predetermined thrust force and/or changes in an axial angle.